The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has been met with advancements in semiconductor manufacturing techniques such as lithography.
For example, the wavelength of radiation used for lithography has decreased from ultraviolet to deep ultraviolet (DUV) and, more recently to extreme ultraviolet (EUV). Further decreases in component size require further improvements in resolution of lithography which are achievable using extreme ultraviolet lithography (EUVL). EUVL employs radiation having a wavelength of about 1-100 nm. Lithography resolution is negatively impacted by diffraction.
Optical proximity correction (OPC) is a photolithography enhancement technique used to compensate for image errors due to diffraction or process effects. The need for OPC is due to the limitations of light to maintain the edge placement integrity of the original design, after processing, into the etched image on the silicon wafer. These projected images appear with irregularities such as line widths that are narrower or wider than designed, these are amenable to compensation by changing the pattern on the photomask used for imaging. Other distortions such as rounded corners are driven by the resolution of the optical imaging tool and are harder to compensate for. Such distortions, if not corrected, may alter the electrical properties of as fabricated devices. Optical proximity correction corrects these errors by moving edges or adding extra polygons to the pattern written on the photomask. Optical proximity correction may use pre-computed look-up tables based on width and spacing between features (known as rule based OPC) or use compact models to dynamically simulate the final pattern and thereby drive the movement of edges, typically broken into sections, to find the best solution (known as model based OPC).
As the semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower costs, there have been challenges in reducing semiconductor feature size.